Cobalt salicylaldehydeethylenediimine and method of production



Patented May 23, 1950 '7 COBALT SALICYLALDE HYDEETHYLENEDI- WIMINENANDJMETHOD F PRODUCTION Melvin Calvin and-- Wendell M? Latimer, Berkeley,

Calif .,r:assignors-: to The JRegentsrof the Univerasi'tyofCalifornia; Berkeley;- ,GaliL; a corp oration "favorable r-economic zit-arms. :proven more?practicalgtherefore to ohtainiicom- 'mercial oxygen through iractionation''ofaliquid air or e1eCtI01ySiScOf'-Wate! "inspite :of: the izfact that such methodsirequireza large investment-.10!

No Drawing. "Application-August 17;1946, Serial Nof6913408 :This invention? relatesto -a-new composition: z:of

unatter, and more particularly; to arnewallotropic J form of cobalt salicylaldehydeethylenediimine;including I methods for pro'ducing the same and methods of substantially continuously producing -oxygen sand nitrogen cyclically from 'the atmosphere" therewith.

There exist systems by whichvoxygenarmay'be 'selectively absorbed from the air under certain absorptionfrom air.

the foregoing conditions.

tion. oioxygen Irom: thaair.

It irhas agenerally capital and-result in the'necessary construction of relatively large units of equipment.

"Commercial processes-'- demand that a chemical intended for use as contemplated must be capable *of reversihly'and rapidly absorbing a significant fraction ofits own' weight of oxygen, andits value for such'use Will -obviously be measured" by'its success in these respects. .n Moreover, it is necessary that the chemical compound finally deteronditions and thenregenerate'd assubstantially e mined .lupcn be composed. ,of., readily v obtainable pure oxygen' bys-a suitable "change o'f condi tions ingredients whosenost. willbear a reasonable re- '-leavin'g'the systemin a state such that a return lationshinto the value,of,theproductfobtained. -to the-orig'in al' conditions Willagaih allow "oxygen The form of the. compound to which this .in-

.vention relates will rapidly and. efliciently.,,absorb Artificially producedcompoundshaving the 'detapproximatelyrteflqb of,its own,weightl of oxygen sired 'characteristicof primarily absorbingwand ,withinlowtemperature and-pressure ranges. retainingandsecondarilyliberating"the*more'or addition, it is estimatedthat approximately 11.5 lessloosely held oxygenhave been madexbywtreatlbs. ,iofloxygenamay begstored per.cubicl foot of ingvarious organic and even inorganiccompounds necessary: equipment. .The liberated, oxygengas under varying conditions of pressure and temper- -m ay.esccwefrom the compoundlwithaiorce equal ature'first to form-oxides and then to-ren'der the to a pressure of. sereralatmospheres under easily --oxides so formed-unstable; generally-by increasing obtainableconditions. 'the-temperatureso as todriveo'if the oxygen asza While: presentlyiknowneless-efiicient solutions are active to absorblandliberate oxygen within Utilizing'the method-of this invention, a desired the -contemplated .ltemperature -ranges herein- "chemical to wit: cobalt salicyladehyde'ethyleneaftenesetiforth,. solidseanalogoustothose oil the min hereinafter "referred t -fic s i-E -iis instant invention a have .required temperatures first combined with a blocking agent-which-upon .ranging-iromeoofito SOOOdegreesC...forsaidpurremoval-under suitable conditions leaves chemical moses, exceptlas hereinafterenoted. bonds whichmay-thenact tofitake upoxygen from It is therefore n O j t of v-thisainvention -t0 the air with a rapidity varying-.withinlclimits in- =.-Dl70i(16 anewandimproved,chemical compeund verselywith .theetemperaturel and directly with v n he desiredrcharacteristics,.describedand t pressure, The oxygen is t giyenflp w t *WhiQh-Q ISQQVPHIbIB of= continu0us cyclicrabsorption a rapidity, and easedependent t uponla reversahof eandsdesotpfionrofr greater-percentage of x n :byaweight "than :has beendieretofore.v obtainable. It is not here intended to review the manifold othero ec is vpro idea wandi pr ved processes which have been heretofore used 221110 fi w rflp und by means of which 1 oxygen achieve a compound of the character described, mayrbebrapm'ly"and emmently gener'fltedvflom "nOris it intended to catalog the-various -comatmosphera pounds ewhichlhaveebeentfound rtoibessuitableain Anethenobjeetls-to provide-aenewrand improved greater or lesser'idegrees; for the purposes -con- 3:33 :31 fii gi f i 22 templated' v nmt'end to micate that lratus;- -panticularlyein relatinelysmall unit instalmanys costly and-elaborate attempts have .been imadelto obtain.improvedchemicalcompounds-of g,Armaher:Objectnof thisrimentiongjsfitoprovide; constantly greater emmency foruselmthe Separa :neweanddm-proved; regenerative chemical 1 com- 'p und:}which; in solid; preferably-s granular form, -Here,toforeitr has-lnot- ,been possible to ,cnemicapable u t uslyrtaking,up -cally generateeoxygenimeany mannerawhich iszcagand fibepatingi oxygen .r .th ,tmosphere at zpablegof' competing withrmechanicalz methods ;OI1 temperatureg ranging from approximatelyu degrees centigrade ;.to approximately -i-30 degrees 'centigradefiove'r "long periods of time: without'lsubstantiakdegeneration orwrlossvof efficiency.

AA?- furtherzobl'ectliseto provideva salidregenera- :1ztiyercherxnica]:of newiand:improvedgranulamform which can continuously and alternately absorb and desorb atmospheric oxygen at various pressures ranging from less than one to several atmospheres and in a temperature range of from degrees C. to 130 degrees 0.

Another further object is to provide a chemical compound usable for the purposes stated, the formula of whose oxygenated form, sometimes referred to herein as the oxide or the oxidized form, is (CmHuOzNzConOu and whose real density is approximately 1.6.

Yet another object is to provide a cobaltous chemical compound having the desirable characteristic herein set forth, whose oxygenated form contains one molecule of 02 for every two atoms active material, and the resultant solution was of cobalt present in said compound and. which can alternately release and reabsorb substantially all of the theoretical amount of oxygen in its oxide under the influence of readily variable and easily obtainable pressure and temperature changes, said compound being capable of withstanding a substantially indefinite number of such cycles without poisoning or substantial deterioration, under suitable conditions.

It is more specifically an object to create a more eiiicient form of cobalt salicylaldehydeethylenediimine, of the general formula than any heretofore known for the purposes herein set forth, said compound having an orthorhombic cell structure and a coplanar stereochemical form in its solid state.

A still further object is to provide a commercially practicable method of producing th desired form of cobalt salicylaldehydeethylenediimine herein described.

Another further object is to provide a commercially suitable method and apparatus for the continuous generation of oxygen from the atmosphere and/ or nitrogen by subtraction.

It is also an object to improve prior art compounds, methods, and apparatus, intended to accomplish a similar purpose.

Other objects and purposes will appear and be more clearly set forth in the following description considered in the light of the appended claims.

Preliminarily, we desire to set forth one example of a preferred procedure for obtaining our desired compound.

In said example 164 grams of 67.9% aqueous ethylenediamine was dissolved in 6.5 liters of commercial ethyl alcohol. To the resultant mixture was added a solution of 576 grams of cobalt acetate, or its equivalent in the form of cobalt chloride and sodium acetate, in 2.9 liters of water.

' To this solution, either at room temperature or at some higher temperature up to 60 degrees C., was added 576 grams of salicylaldehyde. The order of mixing above set forth is merely demonstrative and may be varied in a manner well known to those skilled in the art.

As the last ingredient, salicylaldehyde, was added. the vessel containing the above-mentioned ingredients was closed off and placed under a vacuum pump to remove oxygen from the solution. Said solution was permitted to set for two or three minutes, at the end of which time it appeared as a brown-red gel. Said gel was allowed to stand at room temperature for five or six days during which time it slowly crystallized. It was found that the crystallization time could be cut to less than one day be retaining th gel above normal room temperature, but the accelerated procedure resulted in smaller crystals.

refluxed for approximately two hours, then preferably cooled, as in ice or salt ice, to room temperature and caused to recrystallize at said temperature. The crystals so formed were filtered in-the absence of air, washed with ether and then dried, thereby providing a compound having one molecule of pyridine per atom of cobalt.

These monopyridinate crystals were next heated at a temperature of approximately 160 degrees C. in a preferably rapid stream of air to bring about depyridination, i. e., the removal of the pyridine. The resultant crystalline compound, active to absorb oxygen at readily available temperatures and pressures, was CoSaEn in its most active form, and in its oxygenated state contained one molecule of oxygen for each two atoms of cobalt.

It was found that the actual useful activity of this most active form of CoSaEn was within 97% to 99% of its theoretical capacity to absorb and release oxygen reversibly as defined by its formula. The real density of the material as produced was approximately 1.6. In its powdered state, its density was approximately .3 to .8 depending upon the method of preparation of the powder. It is preferable, however, to compress the material into a cakelike mass and then to break or to crush the cake into the form of small pellets having about three or four times the density of the powder. Such a granular form of the material is generally somewhat porous and takes up oxygen as readily as the powdered form, but is more convenient and practical in use.

In order to verify the actual as compared to the theoretical oxygen-carrying and effective oxygen-generative properties of the most desired form of the material, exhaustive tests were made of which the following example is illustrative:

Wt. of sample after driving off oxygen at 100 degrees C.: 2.369 gm.

Wt. of sample after exposure to oxygen gas:

Wt. of oxygen absorbed: .117 gm. or 4.94%

Wt. 'of sample after oxygen again driven off:

Wt. of oxygen driven o f: .117 gm. or 4.94%

a It will be seen from the above description that a chemical may be prepared having bonds closed by pyridine molecules. In this condition the material can be crystallized. After crystallization has taken place, the pyridine can beremoved without causing any major change in molecular arrangement, and there arethen spaces available for the attachment of oxygen. Thus, the pyridine can be broadly called ablocking agent, which permits the final preparation of the crystalline material to the end that when this blocking agent is subsequently removed by the application of heat, the organic structure becomes active and is able to take up and give off oxygen in accordance with the temperatures and prespreferred values later set forth.

55 ,*isshereinvusedtorillustratezthez in blocking; agentritrziszaintendect to/be merelyillustrative oiablockinglagents in genie er-al which perform a rsimilarzfunction and which; whenaremovedwfrom the ultimatelysdesired compoundnactzto iliberatezbonds sforrthelattachment; ofrroxygenn Thus ;the nmost zpreferrediiformcmay also ;be.1obtained by rapid precipitationfromneue trakz; aqueous :solutions sins: lieu 2 of: pyridine," in: which? casea-theiblo'ckingzagent is? a water mole' -z culeza. Other blocking: ia'gentsiawhichar have" been; usedzi: are npiperidiheg; ethyl: alcohol,,z.and:" propyl alcohol.

As can; alternative :aandreven; morerzppreferable and'sefiicient: :methbdsof: achieving the: most: .de-e; sired .formglthe whole'operationmay beaperiormed: inzcone step to" directly: produce athe; 'monopyrbdiiiate e This mayz besdonerby' mixing;:in .aquee ouscsolution; suitablexproportions: of'ithe =ingredi1-z entsrhereinabove :mentioned;.: to; ;wit :ethylenedi'a amine, cobaltous chloride, and sodium acetate; (orwtheiequivalentii cobaltfiacetate), salicylaldehyde :and: (preferably :lastly) azqu-antity of I pyridine prefera=bly.u corresponding 2 to -at;;least two molecules. of pyridine per atom of. cobalt. By this: procedure; the use. of :talcoholtisf'obviated andithe step f recrystalliz'ing:fromarpyridine is alsorelim inatedi; The dngredientssof: the :desired CoSaEn' compound m-a-y be mixedfiinvpropyl alcoho1 to. obtain a gel whichnfter drying-itself weakly holds wpropyl alcohol'"molecules;- The removal :of these propylalcohol 'blocking I molecules 'by heat ing in air: at a temperature of app-roximatelyrlml degrees 05? again produces the most active form of r'crystallineCoSaEn.

It; appearsdesirable to; note that -theseveral: forms of themampound; while in some instancesa expressible by thesame: chemical formula are wide1y-- differentnot merely in their ability to absorb-oxygen but also ---in their other -pl'l'ysical properties: It has hither-tobeen well known that independent "all'o'tropicforms of the same 'general chemical compound may exist. although the exis'tence of one commonly known" form does not furnish-adequate data upon which to predict the existence-of any other fo'rm; Thusyforexample; diamond-f graphite, and amorphous carbonare all expressible -by the same chemical 'formula or symbol' C," and chemically maybe deemed identical. Itis obvious howeverthat while acciden tally of the same empirical-formula, thesefo'rms are widely different and-"possess utterly distinct: properties and-uses. Thus diamond-may be used for grinding and I cutting, while graphite may be used as a lubricant -'or-refractory. Neither diamond nor- 'graphite;- on= the- -other-"- hand} can function as an adsorbent in tlle manner of char coal! These-three fdrms of carbonaceous =mate=- rial *possess' other---physical differences; inte -the detailsofwhichdt' is not deemed pertinent to ex amine at this -timeexcept to' note' and--underscore tl'ie -fact=that the mere accident- "of" similarity of chemical 'expression of a compound as compared with other compounds doesnot necessarily" esa tablisn the physical identity and equivalence-of saidfdrmsr- Similarly,- there" are several allo tropic io'rms of chemical substances-*difiering -inchemlcal and-physical "properties; but each de scribable as cobaltsalicylaldehydeethylenedi iminer As stated, the *form'is' unaffected by the method of creating the desired :form of CoSaEn as by its said "crystallization directly frorrrpyridineorother solvents Whether or not the blocking agent Em ployew is'rcstricted to-pyridine.

oxygen v in' the oxide.

Inactive, =Less.active Prefeue Form Form Form a- 14.07 6'6 6. 70'- r b: 7.061. t 11.9 v 7. 7 c: 26.1-25 '12.;6.or;25s2 l 25.90

Mono clinic Triclinic orthorhombic The: preferred mostsactive- CoSaEn :compound may also bevutilizedfior-ithe generationwoffoxygenwhi'ledn'pyridine solution; Wh'enzutilized in this manner the. solution maybe rcirculatedibetween highland lowat'emperature;bathseassociated:with

a proper pressure :control-oftz'admixed.:air in suchaamanner that: pyridine:.-is releasedczand oxygen taken upgrathea pyridine and oxygen" being separately trapped iandzzthe pyridine; caused to re-' turn to the solution" as a part ofiithe; generative cycle Thuszit may :be rseenuthat ithezusetofiour compound is'rcapableof'much variationr. and it is, not 'intendedntox limitl "the. utilization thereofvto any. particular method:

Referring nowe briefly to'ia preferred mode "of: use of 'CoSaEIr ll'lfitS most activerandrpreferably granular 'form, the :granules may be placed: in any-"number of: suitable containers-such as tubes; which may: be :positionedi in a heat exchanger and the granules held in place by a porous packing material'in a manner to permit air to pass throughstheltubes and through or over. theigranules at anydesired+pressure Forvthis purpose the tubes may be connected to the atmosphere :through any desired pressure and/or vacuum pumps by way of suitable pipe 'andvyalve systems, all in' a manneranwell knownzto those skilled in theachemical 'or mechanical arts.

In addition appropriate; connections may be made so thatcool-ingand/orheating agents (such asflwater and steam) may alternately be conducted into "the "heatexchanger for circulation around and between the tubes to alternately cool or h'eat the tubes 'andtheir contents as desired. Waste outlets may also be'connectedto the tubes for removing" any oxygen-depleted air fromaround the active CoSaEn material;

It has beerr'found preferable to coolthe inlet air to" approximately 20degrees CI before its passageth'rougn the tubes, and initially to" pro vide" an" excess of air over what the active =-ma'-' terial. can theoreticallytake'up-at the established pressure.

After... passing. r the cooled air over the active material for "a-length oftime sufii'cient td'perm'it it to absorb such a percentage of oxygen as will make an efiicient absorption cycle, the heat exchanger may be discharged of the tap water and chargedwith steam to obtain a tube temperature of approximately 100 degrees C. Thereby the absorbed oxygen will be caused to escape from the active material in the tubes under several atmospheres of pressure whence it may be com ducted to a place of storage or use.

Obviously, a continuous productive cycle of oxygen absorption and desorption can thus be set up, the CoSaEn alternately absorbing oxygen from the air at relatively low temperatures and high pressures and giving up the oxygen under conditions of relatively low pressures and high temperatures.

- Theoxygen desorption at 100 degrees C. is smooth and rapid and can be efficientlyaccomplished in from three to five minutes. The absorption time, as will be seen later, can be reduced to ten minutes, if desired, with about 85% recovery. Usually the absorption time will determine the period of a; complete absorption-desorption cycle, as the desorption time is less than the absorption time for .efiicient recovery at the lower absorption pressures. Thus, a complete cycle, if desired, can be easily reduced to as little as fifteen minutes, including the heating and cooling of the interchanger.

While the dynamics and kinetics of our process will vary somewhat in accordance with the type of heat interchange apparatus used, and the quality and quantity of materials used, the following table may be taken to be representative of the performance of a unit quantity of material in a tubular heat interchanger of the general type described. The absorption temperature in all cases cited is approximately 20 degrees C., and the desorption temperature in all cases cited is approximately 100 degrees C. The oxygen given off was measured in an ordinary gas meter and the desorption time was approximately five minutes in each case. The column of figures below entitled Percent recovery is based upon the maximum amount of oxygen which could be obtained from the unit quantity of CoSaEn after passing oxygen gas through the unit quantity for one hour, and corresponds to a material having 94% of the theoretical activity.

Volume of Air Air passed 02 Percent Pressure Time through Recovery Cubic Feet Hours 20 l 15 86 40 1 16 96 40 E 8 88 80 A 8 98 80 u 4 92 If it is desired to' still further out down the absorption time, the pressure can be raised to 90 pounds, for example, and applied for ten minutes with 10% excess air to give an 85% recovery. Still higher pressures still further reduce the absorption time.

The rate of 02 production per unit weight of active material is greater when operating on the shorter periods. It'will be seen that two fifteen-minute periods at 80 pounds air-pressure will give 184% recovery, whereas three ten-minute periods at 90 pounds air-pressure will give 255% recovery. This shortening of the absorption time, however, is clearly limited by the time required to heat'and cool the material of'the heat exchanger. It has been found, however, that a 15-minute cycle is practical and economical for commercial production of 02.

We have found that'the pressureof oxygen over an oxygenated sample of the compound is about 55 millimeters of mercury at room temperature (22 degrees 0;), one atmosphere at about 58 degrees C., and about six atmospheres at degrees C; The material provides, therefore, sufficient delivery pressure for some practical uses and therefore may be stored without pumping at six atmospheres or less when the 100 degrees C. desorption temperature is utilized, and

at higher pressures, if boosted by a pump or compressor. Obviously, however, if the delivery pressure can be less, as for example one atmosphere, the desorption temperature need only be about 60 degrees C. Therefore higher temperatures can be used to provide higher output pressures.

It can very readily be seen from the above figures that the uptake of oxygen can be controlled in accordance with the applied temperature and pressure, and that the releaseof oxygen can be controlled in accordance with the amount of heat applied to the material. It is not, of course, necessary to use a temperature range of from 20 degrees C. to 100 degrees C. for the regenerative cycle inasmuch as lower, higher, or intermediate temperatures can be utilized in accordance with individual conditions, desired. However, it is believed that the figures given herein will readily make apparent to all those skilled in the art, the manner by which this invention may be applied to any particular problem involving the store and subsequent release of oxygen.

Experiments have been made to determine whether or not the active material is deteriorated by repeated cyclic action thereof. Careful measurements have been made over a large number of cycles performed under controlled conditions, and no appreciable differences could be detected between the action of the material at the end of a single run, and the performance thereof at the beginning of the run. No poisoning occurred but the material could be used to produce approximately 20 lbs. of 02 per pound of CoSaEn before a 50% reduction of its operative efficiency per cycle occurred. crystallized CoSaEn does not react with water at room temperature at any appreciable rate, and while moist air can be used through the material, it is desirable to exclude moisture as far as possible without undue multiplication of equipment or expense. At high temperatures, however, prolonged exposure to steam and oxygen may result in1the reversion of the material to an inactive, inert cobaltic compound; but such an exposure can be readily guarded against, and could not take place except by accident.

While we have described our process so far as being applicable to theselective absorption of pure oxygen from the air, it is obvious that substantially the same general type of apparatus can be utilized to selectively absorb oxygen from a mixture of gases. However, when our process is utilized for the selective absorption of oxygen from atmospheric air, it'will be obvious that the air that has passed through the heat exchanger, as above described, has had a large percentage of its oxygen removed from it. The percentage of nitrogen remaining in the output air is therefore high.

Reference to a "molecule? of oxygen in this specification and claims is intended to denote one molecule of oxygen consisting of two atoms.

The gist of this invention is the production of a new form of CoSaEn and the alternate and continuous absorption and desorption of atmospheric oxygen therewith.

Although we have herein described our invention and its mode of production, application and use in what we deem to be its most preferred mode and form, departures may be made therefrom without departing from the spirit of the invention as expressed in the appended claims.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

1. The formation of a preferred allotropic crystalline form of cobalt salicylaldehydeethylenediimine in its non-oxygenated state by the steps of combining aqueous ethylenediamine, ethyl alcohol, cobalt acetate, water and salicylaldehyde in the absence of air to form a gel; crystallizing said gel; dissolving the resultant crystals in a solution comprising a blocking agent selected from the group consisting of propyl alcohol and pyridine; recrystallizing said dissolved material; filtering, washing and drying the recrystallized material in the absence of air to form crystals containing said blocking agent; and removin said blocking agent by heating said recrystallized material to an elevated temperature is a stream of air to preclude combination of oxygen therewith.

2. The formation of a preferred allotropic crystalline form of cobalt salicylaldehydeethylenediimine in its non-oxygenated state by the steps of combining aqueous ethylenediamine, ethyl a1- cohol, cobalt acetate, water and salicylaldehyde in the absence of air to form a gel; crystallizing said gel; dissolving the resultant crystals in a solution of pyridine; recrystallizing said dissolved material from said pyridine solution; filtering, washing and drying the recrystallized material in the absence of air to form monopyridinate crystals; and depyridinating said monopyridinate crystals by heating said crystals in a stream of air at approximately 160 degrees centigrade so as to preclude combination of oxygen with said crystals.

3. The formation of a preferred allotropic crystalline form of cobalt salicylaldehydeethylenediimine in its non-oxygenated state by the steps of combining aqueous ethylenediamine, ethyl alcohol, cobalt acetate, water and salicylaldehyde; removing oxygen from said mixture in the absence of air to form a gel; crystallizing said gel; dissolving the resultant crystals in a solution comprising propyl alcohol; recrystallizing said dissolved material from said alcohol solution;

filtering, washing and drying the recrystallized material in the absence of air to form said cobalt salicylaldehydeethylenediimine combined with propyl alcohol; and removing said propyl alcb} hol by heating the crystals at approximately degrees centigrade in a stream of air to pref-j clude the combination of oxygen with said cobalt salicylaldehydethylenediimine.

4. The method of producing a preferred active form of cobalt salicylaldehydeethylenediimine comprising mixing ethylenediamine, salicylalde-j hyde, a cobaltous salt and pyridine in aqueous solution to crystallize therefrom cobalt salicylaldehydeethylenediimine combined with the pyridine, and separating said pyridine from said? cobalt salicylaldehydeethylenediimine by heating at approximately 160 degrees centigrade inia stream of air to preclude the combination of oxygen therewith.

5. A chemical compound of orthorhombic cell, structure in its non-oxygenated form, whose molecular measurement is approximately a. 6.70, b. 7.971, c. 25.90, whose empirical formula is," C16H1402N2C0, and which combines with oxygen according to the formula (R0202 where R is C1sH1-1O2N2C0 having a valence of 2.

6. The method of forming a brown orthorhombic, coplanar, crystalline form of cobalt salicylaldehydeethylenediimine, having cell dimensions as follows: a equals 6.70. b equals 7.97, and 0 equals 25.90; comprising the steps of combining ethylenediamine, salicylaldehyde, a cobaltous salt .and pyridine in aqueous solution to crystallize therefrom cobalt salicylaldehydeethylenediimine combined with the pyridine, and heating said crystals in a stream of air at approximatel 160 degrees centigrade.

MELVIN CALVIN.

WENDELL M. LATIMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,091,023 Sinding-Larsen Mar. 24, 1914 1,117,352 Ehrlich Nov. 17, 1914 2,188,746 Bersworth Jan. 30, 1940 2,217,850 Warne Oct. 15, 1940 OTHER REFERENCES Pfeifier et al., "Annalen der Chemie," vol. 503 (1933), pages -126.

Calvin et al., J. Am. Chem. Soc, vol. 68, (Nov. 1946), pages 2254-2256.

Tsumaki-Bull. Chem. Soc. of Japan, vol. 13. 1938, pages 252-260, 379-591. 

1. THE FORMATION OF A PREFERRED ALLOTROPIC CRYSTALLINE FORM OF COBALT SALICYLADEHYDEETHYLENE DIMINE IN ITS NON-OXYGENATED STATE BY THE STEPS OF COMBINING AQUEOUS ETHYLENEDIAMINE, ETHYL ALCOHOL, COBALT ACETATE, WATER AND SALICYLALDEHYDE IN THE ABSENCE OF AIR TO FORM A GEL; CRYSTALLIZING SAID GEL; DISSOLVING THE RESULTANT CRYSTALS IN A SOLUTION COMPRISING A BLOCKING AGENT SELECTED FROM THE GROUP CONSISTING OF PROPYL ALCOHOL AND PYRIDINE; RECRYSTALLIZING SAID DISSOLVED MATERIAL; FILTERING, WASHING AND DRYING THE RECRYSTALLIZED MATERIAL IN THE ABSENCE OF AIR TO FORM CRYSTALS CONTAINING SAID BLOCKING AGENT; AND REMOVING SAID BLOCKING AGENT BY HEATING SAID RECRYSTALLIZED MATERIAL TO AN ELEVATED TEMPERATURE IS A STREAM OF AIR TO PRECLUDE COMBINATION OF OXYGEN THEREWITH. 